Source and drain process for FinFET

ABSTRACT

A FinFET includes a substrate, a fin structure, a dielectric layer, a metal gate, two spacers, a source and a drain. The fin structure is disposed on the substrate. The dielectric layer is disposed on the fin structure and covers two opposite side surfaces of the fin structure. The dielectric layer includes two first portions protruding from the side surfaces of the fin structure, such that two opposite first recesses are formed in the dielectric layer. The metal gate is disposed on a second portion of the dielectric layer which is sandwiched between the first portions. The spacers are disposed on the first portions of the dielectric layer and protrude from the first portions of the dielectric layer respectively, such that two second recesses are formed in the spacers. The source and drain are respectively disposed in the first recesses and the second recesses on the substrate.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. In the course of the IC evolution, functional density (definedas the number of interconnected devices per chip area) has generallyincreased while geometry size (i.e., the smallest component (or line)that can be created using a fabrication process) has decreased. Ascaling down process generally provides benefits by increasingproduction efficiency and lowering associated costs. But, such scalingdown has increased the complexity of processing and manufacturing ICs.For these advances to be realized, similar developments in ICmanufacturing are needed.

For example, as the semiconductor IC industry has progressed intonanometer technology process nodes in pursuit of higher device density,higher performance, and lower costs, challenges from both fabricationand design have resulted in the development of three-dimensional (3D)devices such a fin-like field effect transistors (FinFETs). However,conventional FinFET devices and methods of fabricating the FinFETdevices have not been entirely satisfactory in every aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1A is schematic three-dimensional diagram of a FinFET in accordancewith various embodiments.

FIG. 1B is schematic top view of the FinFET taken along line A-A of FIG.1A.

FIG. 2A through FIG. 2G are three-dimensional diagrams of intermediatestages showing a method for manufacturing a FinFET in accordance withvarious embodiments.

FIG. 3A through FIG. 3G are schematic top views of the FinFET takenalong line A-A of FIG. 2A through 2G respectively.

FIG. 4 is a flow chart of a method for manufacturing a FinFET inaccordance with various embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact.

Terms used herein are only used to describe the specific embodiments,which are not used to limit the claims appended herewith. For example,unless limited otherwise, the term “one” or “the” of the single form mayalso represent the plural form. The terms such as “first” and “second”are used for describing various devices, areas and layers, etc., thoughsuch terms are only used for distinguishing one device, one area or onelayer from another device, another area or another layer. Therefore, thefirst area can also be referred to as the second area without departingfrom the spirit of the claimed subject matter, and the others arededuced by analogy. In addition, the present disclosure may repeatreference numerals and/or letters in the various examples. Thisrepetition is for the purpose of simplicity and clarity and does not initself dictate a relationship between the various embodiments and/orconfigurations discussed. As used herein, the term “and/or” includes anyand all combinations of one or more of the associated listed items.

In a typical FinFET replacement polysilicon gate (RPG) technology with ahigh-k metal gate last (HKMG) process, an operation of removing of aportion of a fin structure and a portion of a dielectric layer coveringthe fin structure needs a high over-etching amount of the fin structureand the dielectric layer, thereby enlarging a process window for each ofsequential deposition process of a high-k dielectric layer and a metalgate, thus enhancing a performance of the FinFET. However, the highover-etching amount of the dielectric layer shortens a portion of thedielectric layer that is used for blocking a dummy gate which covers aportion of the dielectric layer and the underlying fin structure, suchthat an extrusion path is decreased to result in footing of the dummygate, and thus causing a metal gate extrusion issue.

Embodiments of the present disclosure are directed to providing a FinFETand a method for manufacturing the FinFET, in which a first etchingoperation is performed on a fin structure and a dielectric layercovering the fin structure to recess the fin structure and thedielectric layer, so as to form two first recesses respectively in twospacers which cover the dielectric layer and the fin structure, and thena second etching operation is performed on the fin structure to furtherrecess the fin structure to form two second recesses in the dielectriclayer, in which the seconds respectively communicate with the firstrecesses. Thus, portions of the dielectric layer used for blocking adummy gate are lengthened, the dummy gate covering the dielectric layerand the fin structure and being sandwiched between the spacers, suchthat each extrusion path is increased, thereby enhancing the yield ofthe FinFET.

Referring to FIG. 1A and FIG. 1B, FIG. 1A is schematic three-dimensionaldiagram of a FinFET in accordance with various embodiments, and FIG. 1Bis schematic top view of the FinFET taken along line A-A of FIG. 1A. Insome embodiments, a FinFET 100 includes a substrate 102, a fin structure104, a dielectric layer 106, a metal gate 110, two spacers 108, a source112 and a drain 114. The fin structure 104, the dielectric layer 106,the metal gate 110, the spacers 108, the source 112 and the drain 114are disposed on the substrate 102.

The fin structure 104 is disposed on the substrate 102. In someexemplary examples, the fin structure 104 is formed by recessing thesubstrate 102, and thus the fin structure 104 protrudes from a recessedsurface 116 of the substrate 102, and the fin structure 104 and thesubstrate 102 are formed from the same material. The substrate 102 andthe fin structure 104 may be composed of a single-crystallinesemiconductor material or a compound semiconductor material. Forexample, silicon, germanium or glass may be used as a material of thesubstrate 102 and the fin structure 104. In some exemplary examples, thesubstrate 102 and the fin structure 104 are composed of silicon.

Referring to FIG. 1B again, the dielectric layer 106 is disposed on thefin structure 104 and covers two opposite side surfaces 118 of the finstructure 104. The dielectric layer 106 includes two first portions 120,in which the first portions 120 disposed at two opposite ends of thedielectric layer 106. A cross-section of each of the first portions 120is in an inverted U-shape. Each of the first portions 120 of thedielectric layer 106 protrudes from the side surfaces 118 of the finstructure 104 to form a first recess 122 in the dielectric layer 106.Thus, the first recesses 122 are opposite to each other. In someexamples, the fin structure 104 and the dielectric layer 106 are formedfrom different materials, such that the dielectric layer 106 has anetching selectivity with respect to the fin structure 104 during anoperation of etching the fin structure 104. For example, the finstructure 104 may be formed from silicon, and the dielectric layer 106may be formed from silicon oxide.

Referring to FIG. 1A and FIG. 1B, the metal gate 110 is disposed on asecond portion 126 of the dielectric layer 106. In the dielectric layer106, the second portion 126 is adjacent to the first portions 120, inwhich the first portions 120 are located at two opposite ends of thesecond portion 126, such that the second portion 126 is sandwichedbetween the first portions 120. A cross-section of the metal gate 110 isin an inverted U-shape.

As shown in FIG. 1A and FIG. 1B, the spacers 108 are respectivelydisposed on the first portions 120 of the dielectric layer 106. Across-section of each of the spacers 108 is in an inverted U-shape. Thespacers 108 respectively protrude from the first portions 120 of thedielectric layer 106 which are covered by the spacer 108, so as to formtwo second recesses 124 in the spacers 108. The second recesses 124correspondingly communicate with the first recesses 122. In someexamples, the spacers 108 and the fin structure 104 are formed fromdifferent materials, such that the spacers 108 have an etchingselectivity with respect to the fin structure 104 during an operation ofetching the fin structure 104. In some exemplary examples, the spacers108, the dielectric layer 106 and the fin structure 104 are formed fromdifferent materials. For example, the spacers 108 may be formed fromsilicon nitride, while the fin structure 104 may be formed from silicon,and the dielectric layer 106 may be formed from silicon oxide.

As shown in FIG. 1B, the fin structure 104 is further recessed to formthe first recesses 122, such that a length L1 of each spacer 108 isgreater than a length L2 of each second recess 124, and a length L3 of acombination of the first recess 122 and the corresponding second recess124 is greater than the length L1 of each spacer 108. In some exemplaryexamples, the length L1, the length L2 and the length L3 are within arange from 0.5 Å to 100 Å.

As shown in FIG. 1A and FIG. 1B, the source 112 is disposed in one ofthe first recess 122 and the corresponding second recess 124 on thesubstrate 102, and protrudes from the second recess 124. In addition,the drain 114 is disposed in the other one of the first recess 122 andthe corresponding second recess 124 on the substrate 102, and protrudesfrom the second recess 124. In some examples, the source 112 and thedrain 114 may extend through the recessed surface 116 into the substrate102. For example, each of the source 112 and the drain 114 may includean epitaxy layer. In some exemplary examples, the source 112 and thedrain 114 are formed from silicon germanium (SiGe).

Referring to FIG. 1B again, the first recesses 122 are respectivelyformed in the first portions 120 of the dielectric layer 106, such thatextrusion paths of the metal gate 110 are increased with the existenceof the first portions 120 of the dielectric layer 106, and thus themetal gate 110 can be effectively blocked by the first portions 120 ofthe dielectric layer 106, thereby enhancing the yield of the FinFET 100.

Referring to FIG. 2A through FIG. 2G and FIG. 3A through FIG. 3G, FIG.2A through FIG. 2G are three-dimensional diagrams of intermediate stagesshowing a method for manufacturing a FinFET in accordance with variousembodiments, and FIG. 3A through FIG. 3G are schematic top views of theFinFET taken along line A-A of FIG. 2A through 2G respectively. As shownin FIG. 2A and FIG. 3A, a substrate 200 is provided. In some examples,the substrate 200 may be optionally recessed to form a fin structure 202on a surface 204 of the substrate 200 by using, for example, aphotolithography process and an etching process.

In the operation of recessing the substrate 200, a portion of thesubstrate 200 is removed. In such examples, the fin structure 202 iscomposed of a portion of the substrate 200, such that the fin structure202 is formed from a material the same as that of the substrate 200. Thesubstrate 200 and the fin structure 202 may be composed of asingle-crystalline semiconductor material or a compound semiconductormaterial. In some examples, silicon, germanium or glass may be used as amaterial of the substrate 200 and the fin structure 202. In someexemplary examples, the substrate 200 and the fin structure 202 areformed from silicon.

As shown in FIG. 2B and FIG. 3B, a dielectric layer 206 is formed on atop surface 208 and two opposite side surfaces 210 of the fin structure202. In the fin structure 202, the side surfaces 210 are connected totwo opposite edges of the top surface 208. For example, the sidesurfaces 210 may extend along an extending direction of the finstructure. Thus, a cross-section of each of the dielectric layer 206 isin an inverted U-shape. For example, the dielectric layer 206 may beformed by using a deposition process or a thermal oxidation process. Thedeposition process may be a chemical vapor deposition (CVD) process or aplasma-enhanced chemical vapor deposition (PECVD) process. In someexamples, the fin structure 202 and the dielectric layer 206 are formedfrom different materials, such that the dielectric layer 206 has anetching selectivity with respect to the fin structure 202 during anoperation of etching the fin structure 202. For example, the finstructure 202 may be formed from silicon, and the dielectric layer 206may be formed from silicon oxide.

As shown in FIG. 2C and FIG. 3C, a dummy gate 212 is formed on a firstportion 214 of the dielectric layer 206. In some exemplary examples, thedummy gate 212 extends from one of the side surfaces 210 to the otherone of the side surfaces 210 through the top surface 208 of the finstructure 202, such that a cross-section of the dummy gate 212 is in aninverted U-shape. In some examples, the dummy gate 212 is formed byusing a deposition process and an etching process. The depositionprocess may be a chemical vapor deposition process or a plasma-enhancedchemical vapor deposition process, for example. In some exemplaryexamples, the dummy gate 212 is formed from polysilicon.

As shown in FIG. 2D and FIG. 3D, two spacers 216 a and 216 b arerespectively formed on two opposite sidewalls 218 a and 218 b of thedummy gate 212. In some examples, an operation of forming the spacers216 a and 216 b includes forming the spacers 216 a and 216 b on twosecond portions 220 a and 220 b of the dielectric layer 206respectively, and exposing two third portions 222 a and 222 b of thedielectric layer 206. In the dielectric layer 206, the second portion220 a is located between the first portion 214 and the third portion 222a, and the second portion 220 b is located between the first portion 214and the third portion 222 b. For example, the second portions 220 a and220 b are closely adjacent to opposite sides of the first portion 214respectively, and the third portions 222 a and 222 b are closelyadjacent to the second portions 220 a and 220 b respectively.

As shown in FIG. 2D, each of the spacers 216 a and 216 b extends fromone of the side surfaces 210 to the other one of the side surfaces 210through the top surface 208 of the fin structure 202, such that across-section of each of the spacers 216 a and 216 b is in an invertedU-shape. For example, the spacers 216 a and 216 b are formed by using adeposition process and an etching process. The deposition process may bea chemical vapor deposition process or a physical vapor deposition (PVD)process, for example. The etching process may be an etching backprocess. In some examples, the spacers 216 a and 216 b and the finstructure 202 are formed from different materials, such that the spacers216 a and 216 b have an etching selectivity with respect to the finstructure 202 during an operation of etching the fin structure 202. Insome exemplary examples, the spacers 216 a and 216 b, the dielectriclayer 206 and the fin structure 202 are formed from different materials.For example, the spacers 216 a and 216 b may be formed from siliconnitride, while the fin structure 202 may be formed from silicon, and thedielectric layer 206 may be formed from silicon oxide.

Referring to FIG. 3D, a first etching operation is performed on thedielectric layer 206 and the fin structure 202 to remove the thirdportions 222 a and 222 b and a portion of each of the second portions220 a and 220 b of the dielectric layer 206, and two first portions 224a and 224 b of the fin structure 202 underlying the third portions 222 aand 222 b and the portions of the second portions 220 a and 220 b of thedielectric layer 206. As shown in FIG. 2E and FIG. 3E, after the firstetching operation is completed, the spacers 216 a and 216 b respectivelyprotrude from the first portions 220 a and 220 b of the dielectric layer206, so as to form two first recesses 226 a and 226 b in the spacers 216a and 216 b respectively. In some examples, the first etching operationis a high bias etching operation. The first etching operation may beperformed by using a dry etching technique.

Referring to FIG. 3D and FIG. 3E simultaneously, a second etchingoperation is performed on the fin structure 202 to remove two secondportions 228 a and 228 b of the fin structure 202 which are respectivelyadjacent to the first portions 224 a and 224 b of the fin structure 202.As shown in FIG. 2F and FIG. 3F, after the second etching operation iscompleted, the remaining second portions 220 a and 220 b of thedielectric layer 206 protrude from two opposite ends of the finstructure 202 to respectively form second recesses 230 a and 230 b inthe dielectric layer 206. The second recesses 230 a and 230 bcorrespondingly communicate with the first recesses 226 a and 226 b. Insome examples, the second etching operation is a high selectivityetching operation, and the dielectric layer 206 has an etchingselectivity with respect to the fin structure 202 during the secondetching operation. Thus, a cross-section of each of the second portions220 a and 220 b of the dielectric layer may be in an inverted U-shapeafter the second etching operation is completed. The second etchingoperation may be performed by using a dry etching technique.

Referring to FIG. 3F again, with a two-step etching process, the finstructure 202 is further recessed to form the second recesses 230 a and230 b during the second etching operation, such that a length D1 of eachof the spacers 216 a and 216 b is greater than a length D2 of each ofthe first recesses 226 a and 226 b, and a length D3 of a combination ofthe first recess 226 a and the second recess 230 a or a combination ofthe first recess 226 b and the second recess 230 b is greater than thelength D1 of each of the spacers 216 a and 216 b. In some exemplaryexamples, the length D1, the length D2 and the length D3 are within arange from 0.5 Å to 100 Å.

By using a two-step etching process, the second recesses 230 a and 230 bare respectively formed in the second portions 220 a and 220 b of thedielectric layer 206, such that extrusion paths of the dummy gate 212are increased with the existence of the second portions 220 a and 220 bof the dielectric layer 206, and thus the dummy gate 212 can beeffectively blocked by the second portions 220 a and 220 b of thedielectric layer 206.

In some examples, after the second etching operation is completed, a wetclean operation may be optionally performed on the first recesses 226 aand 226 b and the second recesses 230 a and 230 b to remove particles,products and/or contaminants from the first recesses 226 a and 226 b andthe second recesses 230 a and 230 b. During the wet clean operation, thedummy gate 212 can be effectively protected by the second portions 220 aand 220 b of the dielectric layer 206, thereby preventing the dummy gate212 from extruding.

As shown in FIG. 2G and FIG. 3G, a source 232 may be formed in the firstrecess 226 a and the second recess 230 a on the substrate 200, and adrain 234 may be formed in the first recess 226 b and the second recess230 b on the substrate 200. For example, the source 232 may be formed tofill the first recess 226 a and the second recess 230 a and protrudefrom the spacer 216 a, such that the source 232 may cover a portion ofan outer surface 236 a of the spacer 216 a and a portion of the surface204 of the substrate 200. The drain 234 may be formed to fill the firstrecess 226 b and the second recess 230 b and protrude from the spacer216 b, such that the drain 234 may cover a portion of an outer surface236 b of the spacer 216 b and a portion of the surface 204 of thesubstrate 200. In some examples, an operation of forming the source 232and the drain 234 is performed by using an epitaxy process. In someexemplary examples, each of the source 232 and the drain 234 is formedto include a silicon germanium (SiGe) layer.

Referring to FIG. 2F and FIG. 2G simultaneously, after the source 232and the drain 234 are completed, the dummy 212 are replaced with a metalgate 238 to complete a FinFET 240. In some examples, an operation ofreplacing the dummy gate 212 includes removing the dummy gate 212 toform a recess between the spacers 216 a and 216 b and expose the firstportion 214 of the dielectric layer 206, and forming the metal gate 238fill the recess and cover the first portion 214 of the dielectric layer206. For example, an operation of removing the dummy gate 212 may beperformed using a dry etching technique or a wet etching technique. Anoperation of forming the metal gate 238 may be performed by using adeposition process and a patterning process, in which the depositionprocess may be a chemical vapor deposition process or a physical vapordeposition process, and the patterning process may include a chemicalmechanical polishing process.

Referring to FIG. 4 with FIG. 2A through FIG. 2G and FIG. 3A throughFIG. 3G, FIG. 4 is a flow chart of a method for manufacturing a FinFETin accordance with various embodiments. The method begins at operation300, where a substrate 200 is provided. In some examples, the substrate200 may be optionally recessed to form a fin structure 202 on a surface204 of the substrate 200 by using, for example, a photolithographyprocess and an etching process. In the operation of recessing thesubstrate 200, a portion of the substrate 200 is removed. In suchexamples, the fin structure 202 is composed of a portion of thesubstrate 200, such that the fin structure 202 is formed from a materialthe same as that of the substrate 200. In some examples, silicon,germanium or glass may be used as a material of the substrate 200 andthe fin structure 202.

At operation 302, as shown in FIG. 2B and FIG. 3B, a dielectric layer206 is formed on a top surface 208 and two opposite side surfaces 210 ofthe fin structure 202. In the fin structure 202, the side surfaces 210are connected to two opposite edges of the top surface 208. For example,the dielectric layer 206 may be formed by using a deposition process ora thermal oxidation process. The deposition process may be a chemicalvapor deposition process or a plasma-enhanced chemical vapor depositionprocess. The fin structure 202 and the dielectric layer 206 are formedfrom different materials, such that the dielectric layer 206 has anetching selectivity with respect to the fin structure 202 during anoperation of etching the fin structure 202.

At operation 304, as shown in FIG. 2C and FIG. 3C, a dummy gate 212 isformed on a first portion 214 of the dielectric layer 206 by using, forexample, a deposition process and an etching process. The depositionprocess may be a chemical vapor deposition process or a plasma-enhancedchemical vapor deposition process. In some exemplary examples, the dummygate 212 extends from one of the side surfaces 210 to the other one ofthe side surfaces 210 through the top surface 208 of the fin structure202, such that a cross-section of the dummy gate 212 is in an invertedU-shape. In some exemplary examples, the dummy gate 212 is formed frompolysilicon.

At operation 306, as shown in FIG. 2D and FIG. 3D, two spacers 216 a and216 b are respectively formed on two opposite sidewalls 218 a and 218 bof the dummy gate 212 by using for example, a deposition process and anetching process. The deposition process may be a chemical vapordeposition process or a physical vapor deposition process. The etchingprocess may be an etching back process. In some examples, an operationof forming the spacers 216 a and 216 b includes forming the spacers 216a and 216 b on two second portions 220 a and 220 b of the dielectriclayer 206 respectively, and exposing two third portions 222 a and 222 bof the dielectric layer 206. In the dielectric layer 206, the secondportion 220 a is located between the first portion 214 and the thirdportion 222 a, and the second portion 220 b is located between the firstportion 214 and the third portion 222 b. For example, the secondportions 220 a and 220 b are closely adjacent to opposite sides of thefirst portion 214 respectively, and the third portions 222 a and 222 bare closely adjacent to the second portions 220 a and 220 brespectively, such that the second portion 220 a is sandwiched betweenthe first portion 214 and the third portion 222 a, and the secondportion 220 b is sandwiched between the first portion 214 and the thirdportion 222 b.

Referring to FIG. 2D again, each of the spacers 216 a and 216 b extendsfrom one of the side surfaces 210 to the other one of the side surfaces210 through the top surface 208 of the fin structure 202, such that across-section of each of the spacers 216 a and 216 b is in an invertedU-shape. In some examples, the spacers 216 a and 216 b and the finstructure 202 are formed from different materials, such that the spacers216 a and 216 b have an etching selectivity with respect to the finstructure 202 during an operation of etching the fin structure 202. Insome exemplary examples, the spacers 216 a and 216 b, the dielectriclayer 206 and the fin structure 202 are formed from different materials.For example, the spacers 216 a and 216 b may be formed from siliconnitride, the fin structure 202 may be formed from silicon, and thedielectric layer 206 may be formed from silicon oxide.

At operation 308, as shown in FIG. 3D, a first etching operation isperformed on the dielectric layer 206 and the fin structure 202 toremove the third portions 222 a and 222 b and a portion of each of thesecond portions 220 a and 220 b of the dielectric layer 206, and twofirst portions 224 a and 224 b of the fin structure 202 underlying thethird portions 222 a and 222 b and the portions of the second portions220 a and 220 b of the dielectric layer 206. In some examples, the firstetching operation is a high bias etching operation. The first etchingoperation may be performed by using a dry etching technique. As shown inFIG. 2E and FIG. 3E, after the first etching operation is completed, thespacers 216 a and 216 b respectively protrude from the first portions220 a and 220 b of the dielectric layer 206, so as to form two firstrecesses 226 a and 226 b in the spacers 216 a and 216 b respectively.

At operation 310, referring to FIG. 3D and FIG. 3E simultaneously, asecond etching operation is performed on the fin structure 202 to removetwo second portions 228 a and 228 b of the fin structure 202 which arerespectively adjacent to the first portions 224 a and 224 b of the finstructure 202. As shown in FIG. 2F and FIG. 3F, after the second etchingoperation is completed, the remaining second portions 220 a and 220 b ofthe dielectric layer 206 protrude from two opposite ends of the finstructure 202 to respectively form second recesses 230 a and 230 b inthe dielectric layer 206. The second recesses 230 a and 230 brespectively communicate with the first recesses 226 a and 226 b. Insome examples, the second etching operation is a high selectivityetching operation, and the dielectric layer 206 has an etchingselectivity with respect to the fin structure 202 during the secondetching operation. Thus, a cross-section of each of the remaining secondportions 220 a and 220 b of the dielectric layer may be in an invertedU-shape. The second etching operation may be performed by using a dryetching technique.

At operation 312, referring to FIG. 2F and FIG. 3F again, after thesecond etching operation is completed, a wet clean operation may beoptionally performed on the first recesses 226 a and 226 b and thesecond recesses 230 a and 230 b to remove particles, products and/orcontaminants from the first recesses 226 a and 226 b and the secondrecesses 230 a and 230 b. During the wet clean operation, the dummy gate212 can be effectively protected by the second portions 220 a and 220 bof the dielectric layer 206, thereby preventing the dummy gate 212 fromextruding.

At operation 314, as shown in FIG. 2G and FIG. 3G, a source 232 may beformed in the first recess 226 a and the second recess 230 a on thesubstrate 200, and a drain 234 may be formed in the first recess 226 band the second recess 230 b on the substrate 200 by using an epitaxyprocess. For example, the source 232 may be formed to fill the firstrecess 226 a and the second recess 230 a and protrude from the spacer216 a, such that the source 232 may cover a portion of an outer surface236 a of the spacer 216 a and a portion of the surface 204 of thesubstrate 200. The drain 234 may be formed to fill the first recess 226b and the second recess 230 b and protrude from the spacer 216 b, suchthat the drain 234 may cover a portion of an outer surface 236 b of thespacer 216 b and a portion of the surface 204 of the substrate 200. Insome exemplary examples, each of the source 232 and the drain 234 isformed to include a silicon germanium layer.

At operation 316, referring to FIG. 2F and FIG. 2G simultaneously, afterthe epitaxy process is completed, the dummy 212 are replaced with ametal gate 238 to complete a FinFET 240. In some examples, an operationof replacing the dummy gate 212 includes removing the dummy gate 212 toform a recess between the spacers 216 a and 216 b and expose the firstportion 214 of the dielectric layer 206, and forming the metal gate 238fill the recess and cover the first portion 214 of the dielectric layer206. For example, an operation of removing the dummy gate 212 may beperformed using a dry etching technique or a wet etching technique. Anoperation of forming the metal gate 238 may be performed by using adeposition process and a patterning process, in which the depositionprocess may be a chemical vapor deposition process or a physical vapordeposition process, and the patterning process may include a chemicalmechanical polishing process.

In accordance with an embodiment, the present disclosure discloses amethod for manufacturing a FinFET. In this method, a fin structure isformed on a substrate. A dielectric layer is formed on a top surface andtwo side surfaces of the fin structure, in which the side surfaces areconnected to two opposite edges of the top surface, and the finstructure and the dielectric layer are formed from different materials.A dummy gate is formed on a first portion of the dielectric layer. Twospacers are respectively formed on two opposite sidewalls of the dummygate. An operation of forming the spacers includes forming the spacersrespectively on two second portions of the dielectric layer and exposingtwo third portions of the dielectric layer, in which each of the secondportions of the dielectric layer is located between the first portionand one of the third portions of the dielectric layer. A first etchingoperation is performed on the dielectric layer and the fin structure toremove the third portions and a portion of each of the second portionsof the dielectric layer, and two first portions of the fin structureunderlying the third portions and the portions of the second portions ofthe dielectric layer, thereby forming two first recesses respectively inthe spacers. A second etching operation is performed on the finstructure to remove two second portions of the fin structure which arerespectively adjacent to the first portions of the fin structure,thereby forming two second recesses in the dielectric layer, in whichthe second recesses respectively communicate with the first recesses.

In accordance with another embodiment, the present disclosure disclosesa method for manufacturing a FinFET. In this method, a fin structure isformed on a substrate. A dielectric layer is formed on a top surface andtwo side surfaces of the fin structure, in which the side surfaces areconnected to two opposite edges of the top surface, and the finstructure and the dielectric layer are formed from different materials.A dummy gate is formed on a first portion of the dielectric layer. Twospacers are respectively formed on two opposite sidewalls of the dummygate. An operation of forming the spacers includes forming the spacersrespectively on two second portions of the dielectric layer and exposingtwo third portions of the dielectric layer, in which each of the secondportions of the dielectric layer is located between the first portionand one of the third portions of the dielectric layer. A first etchingoperation is performed on the dielectric layer and the fin structure toremove the third portions of the dielectric layer, a portion of each ofthe second portions of the dielectric layer, and two first portions ofthe fin structure underlying the third portions of the dielectric layerand the portions of the second portions of the dielectric layer, therebyforming two first recesses respectively in the spacers. A second etchingoperation is performed on the fin structure to remove two secondportions of the fin structure which are respectively adjacent to thefirst portions of the fin structure, thereby forming two second recessesin the dielectric layer, wherein the second recesses respectivelycommunicate with the first recesses. A wet clean operation is performedon the first recesses and the second recesses. An epitaxy operation isperformed on the substrate to form a source in one of the first recessesand one of the second recesses on the substrate, and to form a drain inthe other one of the first recesses and the other one of the secondrecesses on the substrate.

In accordance with yet another embodiment, the present disclosurediscloses a FinFET. The FinFET includes a substrate, a fin structure, adielectric layer, a metal gate, two spacers, a source and a drain. Thefin structure is disposed on the substrate. The dielectric layer isdisposed on the fin structure and covers two opposite side surfaces ofthe fin structure, in which the dielectric layer includes two firstportions protruding from the side surfaces of the fin structure, suchthat two first recesses are formed in the dielectric layer, and thefirst recesses are opposite to each other. The metal gate is disposed ona second portion of the dielectric layer, in which the second portion issandwiched between the first portions of the dielectric layer. Thespacers are disposed on the first portions of the dielectric layerrespectively, in which the spacers respectively protrude from the firstportions of the dielectric layer, such that two second recesses areformed in the spacers. The source is disposed in one of the firstrecesses and one of the second recesses on the substrate. The drain isdisposed in the other one of the first recesses and the other one of thesecond recesses on the substrate.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for manufacturing a FinFET, the methodcomprising: forming a fin structure on a substrate; forming a dielectriclayer on a top surface and two side surfaces of the fin structure,wherein the side surfaces are connected to two opposite edges of the topsurface, and the fin structure and the dielectric layer are formed fromdifferent materials; forming a dummy gate on a first portion of thedielectric layer; forming two spacers respectively on two oppositesidewalls of the dummy gate, wherein an operation of forming the spacerscomprises forming the spacers respectively on two second portions of thedielectric layer and exposing two third portions of the dielectriclayer, wherein each of the second portions of the dielectric layer islocated between the first portion and one of the third portions of thedielectric layer; performing a first etching operation on the dielectriclayer and the fin structure to remove the third portions and a portionof each of the second portions of the dielectric layer, and two firstportions of the fin structure underlying the third portions and theportions of the second portions of the dielectric layer, thereby formingtwo first recesses respectively in the spacers; and performing a secondetching operation on the fin structure to remove two second portions ofthe fin structure which are respectively adjacent to the first portionsof the fin structure, thereby forming two second recesses in thedielectric layer, wherein the second recesses respectively communicatewith the first recesses.
 2. The method of claim 1, wherein an operationof forming the fin structure forms the fin structure from silicon, andan operation of forming the dielectric layer forms the dielectric layerfrom silicon oxide.
 3. The method of claim 1, wherein the operation offorming the spacers forms the spacers from silicon nitride.
 4. Themethod of claim 1, wherein an operation of forming the dummy gate formsthe dummy gate from polysilicon.
 5. The method of claim 1, the methodfurther comprising performing a wet clean operation on the firstrecesses and the second recesses after the second etching operation iscompleted.
 6. The method of claim 1, the method further comprisingperforming an epitaxy operation on the substrate to form a source in oneof the first recesses and one of the second recesses on the substrate,and to form a drain in the other one of the first recesses and the otherone of the second recesses on the substrate after the second etchingoperation is completed.
 7. The method of claim 6, wherein the epitaxyoperation forms the source and the drain each of which comprises asilicon germanium (SiGe) layer.
 8. The method of claim 6, the methodfurther comprising replacing the dummy gate with a metal gate after theepitaxy operation is completed.
 9. A method for manufacturing a FinFET,the method comprising: forming a fin structure on a substrate; forming adielectric layer on a top surface and two side surfaces of the finstructure, wherein the side surfaces are connected to two opposite edgesof the top surface, and the fin structure and the dielectric layer areformed from different materials; forming a dummy gate on a first portionof the dielectric layer; forming two spacers respectively on twoopposite sidewalls of the dummy gate, wherein an operation of formingthe spacers comprises forming the spacers respectively on two secondportions of the dielectric layer and exposing two third portions of thedielectric layer, wherein each of the second portions of the dielectriclayer is located between the first portion and one of the third portionsof the dielectric layer; performing a first etching operation on thedielectric layer and the fin structure to remove the third portions ofthe dielectric layer, a portion of each of the second portions of thedielectric layer, and two first portions of the fin structure underlyingthe third portions of the dielectric layer and the portions of thesecond portions of the dielectric layer, thereby forming two firstrecesses respectively in the spacers; performing a second etchingoperation on the fin structure to remove two second portions of the finstructure which are respectively adjacent to the first portions of thefin structure, thereby forming two second recesses in the dielectriclayer, wherein the second recesses respectively communicate with thefirst recesses; performing a wet clean operation on the first recessesand the second recesses; and performing an epitaxy operation on thesubstrate to form a source in one of the first recesses and one of thesecond recesses on the substrate, and to form a drain in the other oneof the first recesses and the other one of the second recesses on thesubstrate.
 10. The method of claim 9, wherein an operation of formingthe fin structure forms the fin structure from silicon, and an operationof forming the dielectric layer forms the dielectric layer from siliconoxide.
 11. The method of claim 9, wherein the operation of forming thespacers forms the spacers from silicon nitride.
 12. The method of claim9, wherein an operation of forming the dummy gate forms the dummy gatefrom polysilicon.
 13. The method of claim 9, wherein the epitaxyoperation is performed to form the source and the drain each of whichcomprises a silicon germanium (SiGe) layer.
 14. The method of claim 9,wherein an operation of forming the fin structure is performed byrecessing the substrate.
 15. The method of claim 9, the method furthercomprising replacing the dummy gate with a metal gate after the epitaxyoperation is completed.
 16. A FinFET comprising: a substrate; a finstructure on the substrate; a dielectric layer which is disposed on thefin structure and covers a top surface and two opposite side surfaces ofthe fin structure, wherein the dielectric layer comprises two firstportions protruding from the side surfaces of the fin structure suchthat two first recesses are formed in the dielectric layer, each of thefirst recesses is surrounded by the dielectric layer and the substrate,and the first recesses are opposite to each other; a metal gate on asecond portion of the dielectric layer, wherein the second portion issandwiched between the first portions of the dielectric layer; twospacers on the first portions of the dielectric layer respectively,wherein the spacers respectively protrude from the first portions of thedielectric layer such that two second recesses are formed in thespacers; a source which is disposed in one of the first recesses and oneof the second recesses on the substrate; and a drain which is disposedin the other one of the first recesses and the other one of the secondrecesses on the substrate.
 17. The FinFET of claim 16, wherein the finstructure is formed from silicon, and the dielectric layer is formedfrom silicon oxide.
 18. The FinFET of claim 16, wherein the spacers areformed from silicon nitride.
 19. The FinFET of claim 16, wherein thesource and the drain are formed from silicon germanium.
 20. The FinFETof claim 16, wherein each of the source and the drain comprises anepitaxy layer.